The present invention relates to the field of photography and, more specifically, to a photographic apparatus or adapter for use with a large format self-developing film processor for receiving a cassette holding an exposed film unit, for supporting the cassette an an operative position relative to a film entry on the processor and for releasing a latched pressure device on the cassette to substantially reduce pressure applied to the film unit and thereby facilitate its advancement from the cassette into the processor.
Certain types of self-developing film units, for example the large format (e.g. 8.times.10 or larger) type for conventional or X-ray photography, include separate image recording and image receiving sheets.
In use, the photosensitive image recording sheet is loaded into a cassette which is then mounted on a large format view camera or X-ray apparatus for film exposure. Thereafter the cassette is transferred to a receiving tray or adapter mounted on a film processor where the exposed sheet has its leading end coupled to the leading end of an underlying image receiving sheet located in the adapter. The coupled sheets are then advanced in superposed relation into the processor and between a pair of pressure applying rollers which rupture a container, on the image receiving sheet, holding a supply of fluid processing composition and distribute the fluid between the superposed sheets to initiate a well-known development and diffusion transfer process. Following a suitable imbibition period, the sheets are separated to reveal a positive image print on the image receiving sheet.
Generally, the photosensitive image recording sheet is initially provided in a protective opaque envelope which is withdrawn from the cassette through a light sealed end opening after the cassette is closed to render it light tight. Therefore, to facilitate withdrawal of the envelope (and later the exposed image recording sheet) it is desirable that the structure of the closed cassette not apply any appreciable force or pressure on the sheet which would inhibit its advancement in a direction parallel to an internal film bearing surface that defines a film plane within the cassette. On the other hand, it is most desirable that the film unit have sufficient pressure applied thereto to urge it into intimate contact with the bearing surface to accurately locate it at the film plane for exposure. Additionally, in those cassettes designed for radiographic applications, such pressure is also utilized to urge an intensifying screen, within the cassette, into intimate contact with an X-ray sensitive recording sheet to enhance image formation.
Cassettes designed for such applications generally have some type of pressure applying mechanism or pressure plate that is releasably latched in a pressure applying position for exposure and then is unlatched to relieve the pressure to facilitate film withdrawal.
One such cassette has a pressure latching system that is designed to cooperate with latch release structure on the cassette receiving tray for automatically unlatching the pressure applying device in response to locating the cassette at an operative position thereon wherein the film withdrawal slot at one end of the cassette faces the entry opening of the processor in preparation for film processing.
As described in commonly-assigned U.S. Pat. No. 4,156,568 and copending application U.S. Ser. No. 841,889 filed on Oct. 13, 1977 by Herman E. Erikson and entitled "X-ray Cassette For Large Format Film", now U.S. Pat. No. 4,186,308, this cassette includes an internal pressure plate that presses an intensifying screen against the film unit, after the opaque envelope has been withdrawn, in response to manually moving a slide handle to set a pair of longitudinally extending internal latch rods in a pressure applying latching position. The cassette receiving tray mounted on the processor includes a pair of rearwardly extending latch release pins at the forward end of the tray which extend into a pair of openings on the leading end wall of the cassette and push the latch rods rearwardly to an unlatching position in response to sliding the cassette forwardly in the tray to a fully inserted operative position.
The present invention is directed to a photographic apparatus or cassette receiving adapter that is specifically designed for use with an improved large format film cassette of the type described and claimed in commonly-assigned copending application U.S. Ser. No. 108,457 filed on even date herewith by Daniel A. Buldini and Donald Richards and entitled "Cassette For Large Format Film Unit". The disclosure in said application is incorporated herein by reference.
Unlike the previously-noted cassette (Ser. No. 841,889), this cassette eliminates the need for a separate pressure plate and therefor is less complex, easier to manufacture and less costly. Instead, the cassette base and cover sections that are coupled together in telescoping relation for movement toward and away from one another in a direction transverse to the film plane between a first closed position where there is minimal pressure applied to the film unit to permit envelope and film withdrawal and a second closed position wherein the base and cover sections are closer together and sufficient pressure is applied to urge the film unit into intimate contact with a film bearing surface and to urge an intensifying screen into intimate contact with the film unit. Thus the cover section acts both as a component of the cassette housing and a pressure applying device.
To releasably latch the cassette components in the second closed position, the cassette utilizes independently operable longitudinally spaced forward and rear latching devices which are forwardly biased into a latching position and are adapted to be released by sliding cooperating forward and rear longitudinally spaced pressure latch release members, disposed on exterior side wall portions of the cover section, rearwardly to an unlatching position. Accordingly, there is a need for a cassette receiving adapter that includes structure for automatically actuating these release members to release the pressure on the film unit in preparation for film withdrawal.
Therefore, it is an object of the invention to provide a photographic apparatus for use with a film processor for receiving and supporting such a cassette and for automatically actuating the forward and rear latch release members in response to locating the cassette at an operative position on the apparatus.
It is another object to provide such an apparatus that is simple in its construction and operation.
Another object is to provide an apparatus which is configured to effect the release of the forward and rear cassette latches substantially simultaneously.
Yet another object is to provide such an apparatus that releasably retains the cassette at its operative position when the spring biased forward and rear latches are moved to the unlatching position.
Still another object is to provide such an apparatus that allows the cassette to be slidingly advanced into a cassette receptacle without prematurely actuating either one of the forward and rear latch release members.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.